I love the first Doctor's speech at the end of "The Dalek Invasion of Earth" - when Susan leaves. It's almost Churchillian.

One day I shall come back, yes I shall come back. Until then, there must be no tears, no anxieties. Just go forward in all your beliefs, and prove to me that I am not mistaken in mine.

A fantastic moment.

I'd also like to nominate Ghost Light ...

I can't stand burnt toast. I loathe bus stations. Terrible places, full of lost luggage and lost souls. Then there's unrequited love, and tyranny, and cruelty. We all have a universe of our own terrors to face

And the Doctor's final words in Survival ...

There are worlds out there where the sky is burning, where the sea is asleep and the rivers dream; people made of smoke and cities made of song. Somewhere there's danger, somewhere there's injustice, and somewhere else the tea is getting cold. Come on, Ace, we've got work to do.

Also loved the Second Doctor's speech in the Moonbase about Evil in the Universe which must be fought.

"There are some corners of the universe which have bred the most terrible things. Things which act against everything we believe in. They must be fought."

It's an interesting line that, as it marks the exact point at which the Doctor stopped being merely a curious explorer of space and time, befuddled by how the TARDIS operated and never really ending up where he wanted to go. With this quote, Gerry Davis and Innes Lloyd have transformed the Doctor into a moral crusader, a man who pits himself against the 'baddies' purely because they are Bad. The moral ambiguity of Hartnell is swept away, and from now on Troughton fights Monsters, who 'must be fought' solely because they are monsters. To a large degree, this view of the Doctor has continued ever since.

As much as love the big speeches (One in Dalek Invasion of Earth, Four in The Ark of Space, Eleven in Rings of Akhaten and the speech to little Amelia in The Big Bang), I have to mention this less prominent one from Eleven:

"All the elements in your body were forged many, many millions of years ago in the heart of a far away star that exploded and died. That explosion scattered those elements across the desolation of deep space. After so, so many millions of years these elements came together to form new stars and new planets and on and on it went. The elements came together and burst apart forming shoes and ships and sealing wax and cabbages and kings ... until eventually they came together to make you. You are unique in the Universe."

"There are some corners of the universe which have bred the most terrible things. Things which act against everything we believe in. They must be fought."

It's an interesting line that, as it marks the exact point at which the Doctor stopped being merely a curious explorer of space and time, befuddled by how the TARDIS operated and never really ending up where he wanted to go. With this quote, Gerry Davis and Innes Lloyd have transformed the Doctor into a moral crusader, a man who pits himself against the 'baddies' purely because they are Bad. The moral ambiguity of Hartnell is swept away, and from now on Troughton fights Monsters, who 'must be fought' solely because they are monsters. To a large degree, this view of the Doctor has continued ever since.

Great post and a really good insight. Steven Moffat has observed that 'The Dalek Invasion of Earth' was the first story to firmly establish the Doctor as an unambiguously heroic character who fights evil, but you're right - this speech really codifies it, as does the Troughton era generally. I really appreciate episodes which bring back some of that earlier nuance and somewhat less of the parochial moralism encapsulated in this speech.

One day I shall come back, yes I shall come back. Until then, there must be no tears, no anxieties. Just go forward in all your beliefs, and prove to me that I am not mistaken in mine.

A fantastic moment.

Except he then undoes it by resolutely never going back to her, proving he was pulling all kinds of B.S out of his arse just to make her feel better about being abandoned by her own flesh and blood!
Nice guy, the first!

I liked Rose's speech in "The Parting of the Ways" about how the Doctor was fighting for the universe as they talked even though it was in the future, and how he shows you a better way of living your life, standing up for what's right even if it's in the face of evil.

Iím not running away. But this is one cornerÖ of one country, in one continent, on one planet thatís a corner of a galaxy thatís a corner of a universe that is forever growing and shrinking and creating and destroying, and never remaining the same for a single millisecond. And there is so much, so much to see, Amy. Because it goes so fast. Iím not running away from things, I am running to them. Before they flare and fade forever... and itís all right. Our lives wonít run the same. They canít.

One day I shall come back, yes I shall come back. Until then, there must be no tears, no anxieties. Just go forward in all your beliefs, and prove to me that I am not mistaken in mine.

A fantastic moment.

I'd also like to nominate Ghost Light ...

I can't stand burnt toast. I loathe bus stations. Terrible places, full of lost luggage and lost souls. Then there's unrequited love, and tyranny, and cruelty. We all have a universe of our own terrors to face

And the Doctor's final words in Survival ...

There are worlds out there where the sky is burning, where the sea is asleep and the rivers dream; people made of smoke and cities made of song. Somewhere there's danger, somewhere there's injustice, and somewhere else the tea is getting cold. Come on, Ace, we've got work to do.

A bit of a poet, the Seventh Doctor.

All great. I've always liked McCoy's Doctor, and, Survival apart, I haven't seen any McCoy episodes for ages. I want to go back and watch them now. Well, apart from The Happiness Patrol...

'He's like fire, and ice, and rage...' The Family of Blood

The Second Doctor's reflections on his family in Tomb of the Cybermen - just lovely.

Rose's speech in The Parting of the Ways on making a stand, and the Ninth Doctor's last speech before regenerating, are IMO amongst the best dialogue ever written for the show.

Martha's speech in Last of the Time Lords,where she laughs at, and undermines, the Master, is also brilliant IMO.

'...I believe in her!' The Satan Pit. Ten at his (brilliant!) best, IMO.